Can You Waterproof Just the Bathroom Floor? is essential reading for anyone planning a bathroom renovation or new build in Perth. Bathroom waterproofing is one of the most critical building processes in any home, yet it remains one of the most frequently defective. In Perth, where sandy soils and high water tables can compound moisture problems, getting bathroom waterproofing right the first time is not optional — it is essential for protecting your property and your health.
Laundry Waterproofing Requirements
Laundries are classified as wet areas under AS 3740 and require waterproofing to the same standard as bathrooms. The entire laundry floor must be waterproofed, with the membrane extending at least 150mm up all walls. This includes areas behind and beside washing machines, under laundry tubs, and around all plumbing penetrations.
Many Perth homeowners are surprised to learn that laundry waterproofing is mandatory, particularly in renovation projects where the existing laundry may never have been waterproofed. During a renovation, if the floor covering is being replaced or the substrate is being modified, waterproofing must be brought up to current AS 3740 standards. For more information, see our bathroom waterproofing services. This is a legal requirement in Western Australia, not merely a recommendation.
Common laundry waterproofing failures include leaks around washing machine connections, overflow from blocked drains or malfunctioning machines, and condensation from dryers. A properly waterproofed laundry floor with adequate fall to a floor waste protects against all of these scenarios and prevents water damage to adjacent rooms and the building structure below.
AS 3740 Requirements for Wet Areas
AS 3740-2021 is the Australian Standard that governs waterproofing of domestic wet areas. It specifies which areas must be waterproofed, the minimum membrane extent, and the performance requirements that waterproofing systems must meet. In Western Australia, compliance with AS 3740 is mandatory under the National Construction Code and enforced by the WA Building Commission.
Under AS 3740, the entire floor of a shower recess must be waterproofed, with the membrane extending at least 1800mm up all shower walls from the finished floor level. Bathroom floors outside the shower must be waterproofed in their entirety, with the membrane turning up at least 150mm at all walls and junctions. For more information, see our AS 3740 compliance guide. These are minimum requirements — many experienced Perth waterproofers recommend exceeding them for additional protection.
The standard also requires waterproofing around all penetrations, at all internal corners, and at the junction between horizontal and vertical surfaces. Bond-breaker strips must be installed at all internal angles to accommodate building movement. These detailing requirements are where most waterproofing failures occur, making them the most critical aspect of any bathroom waterproofing installation.
Signs of Bathroom Waterproofing Failure
Knowing the early warning signs of waterproofing failure can save thousands of dollars in repair costs by enabling early intervention. Common indicators include persistent musty or mouldy smells in or near the bathroom, even after cleaning. Damp or discoloured patches on walls adjacent to the bathroom, particularly on the other side of shower walls, are another red flag.
Peeling or bubbling paint on the ceiling below a bathroom is one of the most obvious signs of a waterproofing failure above. In multi-storey Perth homes and apartments, ceiling stains below bathrooms are a clear indication that water is penetrating through the floor structure. For more information, see our bathroom waterproofing guide guide. Loose or hollow-sounding tiles, cracked grout that keeps recurring after repair, and swollen or warped skirting boards near the bathroom are all potential indicators of moisture ingress.
If you notice any of these signs, it is important to act quickly. Water damage is progressive — what starts as a minor leak can develop into structural timber rot, extensive mould contamination, and plasterboard deterioration within months. A professional waterproofing inspection can identify the source and extent of the problem and recommend the most cost-effective repair approach.
Waterproofing Before Tiling: Why Sequence Matters
The waterproofing membrane must be fully applied, cured, and flood-tested before any tiling work begins. This is not negotiable under AS 3740 or the NCC. Once tiles are laid over the membrane, there is no practical way to verify membrane integrity without destructive testing, making pre-tile verification essential.
The tiling process itself can damage waterproofing if not done carefully. Tile adhesive must be compatible with the membrane product, and tiles must be laid without puncturing or displacing the membrane. For more information, see our wet area waterproofing requirements guide. In Perth, where large-format tiles are increasingly popular in bathroom renovations, the additional weight and adhesive requirements make membrane compatibility particularly important.
After tiling, the grout and silicone sealant provide the first line of defence against water. However, grout is not waterproof and will eventually crack and deteriorate, allowing water through to the membrane below. This is normal and expected, which is why the underlying membrane is so critical. The membrane is the true waterproofing barrier; the tiles and grout are simply the wearing surface.
Get Expert Help with Your Waterproofing Project
Whether you are planning a new build, renovating an existing property, or dealing with a waterproofing issue that needs urgent attention, working with a licensed professional is the best way to ensure a lasting, compliant result. Perth has many experienced waterproofing contractors who understand the local conditions and can deliver the right solution for your specific needs.
Ready to get started? Use our free tool to find a licensed waterproofer in your area and request obligation-free quotes from vetted professionals. We connect you with licensed contractors who specialise in the type of waterproofing your project requires, so you can compare options and make an informed decision with confidence.